MDEV-41395 fil_space_t::create() may release fil_system.mutex

- By default fil_crypt_must_default_encrypt() holds, and then
fil_crypt_thread() waits indefinitely in wait_for_work() once the
default_encrypt list has been exhausted. A tablespace for which no
fil_crypt_threads_signal() is issued would therefore never be
encrypted at all.

fil_ibd_create(): Invoke fil_crypt_threads_signal() after
fil_space_t::clear_stopped()

dict_load_tablespace(): Invoke fil_crypt_threads_signal(), because
fil_ibd_open() may have added the tablespace to
fil_system.default_encrypt_tables. This is the single point through
which every dictionary-driven tablespace open passes; it is only
invoked by dict_load_table_one(), hence by dict_sys_t::load_table().

The call in dict_table_open_on_name() does not cover it, because
that function returns a cached table before reaching the wake-up.
A table first loaded by dict_table_open_on_id() would thus never be
signalled, neither then nor later.

row_import_cleanup(): Do not invoke fil_crypt_threads_signal().
fil_crypt_add_imported_space() registers it afterwards and broadcasts.

fil_crypt_threads_signal(): Also return early when no encryption
thread is running.

srv_n_fil_crypt_threads_started: Declare as Atomic_relaxed<uint>,
for the unlocked read in fil_crypt_threads_signal().

storage/innobase/dict/dict0load.cc

@@ -2285,6 +2285,14 @@ dict_load_tablespace(
 		fil_space_t::VALIDATE_SPACE_ID,
 		{table->name.m_name, strlen(table->name.m_name)}, filepath);
 
+	/* fil_space_t::create() may have added the tablespace to
+	fil_system.default_encrypt_tables. Signalling here covers
+	every caller of dict_sys_t::load_table() and
+	dict_load_table_on_id(), including dict_table_open_on_name()
+	for a table that some other thread had already loaded into
+	the cache. */
+	fil_crypt_threads_signal();
+
 	if (!table->space) {
 		/* We failed to find a sensible tablespace file */
 		table->file_unreadable = true;

storage/innobase/fil/fil0crypt.cc

@@ -57,7 +57,7 @@ static uint32_t fil_crypt_settings_version;
 uint srv_n_fil_crypt_threads;
 
 /** No of key rotation threads started */
-uint srv_n_fil_crypt_threads_started;
+Atomic_relaxed<uint> srv_n_fil_crypt_threads_started;
 
 /** At this age or older a space/page will be rotated */
 uint srv_fil_crypt_rotate_key_age;
@@ -104,7 +104,7 @@ static mysql_mutex_t crypt_stat_mutex;
 /** Wake up the encryption threads */
 void fil_crypt_threads_signal(bool broadcast)
 {
-  if (!fil_crypt_threads_inited)
+  if (!fil_crypt_threads_inited || !srv_n_fil_crypt_threads_started)
     return;
   mysql_mutex_lock(&fil_crypt_threads_mutex);
   if (broadcast)
@@ -2185,7 +2185,7 @@ static void fil_crypt_thread()
 	pfs_register_thread(page_encrypt_thread_key);
 #endif /* UNIV_PFS_THREAD */
 	mysql_mutex_lock(&fil_crypt_threads_mutex);
-	rotate_thread_t thr(srv_n_fil_crypt_threads_started++);
+	rotate_thread_t thr(srv_n_fil_crypt_threads_started.fetch_add(1));
 	pthread_cond_broadcast(&fil_crypt_cond);
 
 	if (!thr.should_shutdown()) {
@@ -2319,7 +2319,7 @@ restart_iteration:
 		}
 	}
 func_exit:
-	srv_n_fil_crypt_threads_started--;
+	srv_n_fil_crypt_threads_started.fetch_sub(1);
 	pthread_cond_broadcast(&fil_crypt_cond);
 	mysql_mutex_unlock(&fil_crypt_threads_mutex);
 

storage/innobase/fil/fil0fil.cc

@@ -2024,7 +2024,6 @@ fil_ibd_create(
 	fil_node_t* node = space->add(path, OS_FILE_CLOSED, size, false, true);
 	space->set_stopped();
 	mysql_mutex_unlock(&fil_system.mutex);
-	fil_crypt_threads_signal();
 
 	buf_block_t *header[2];
 	{
@@ -2134,6 +2133,7 @@ func_exit:
 		space->release();
 	}
 	mysql_mutex_unlock(&fil_system.mutex);
+	fil_crypt_threads_signal();
 	goto func_exit;
 }
 

storage/innobase/include/srv0srv.h

@@ -210,7 +210,7 @@ extern uint32_t srv_undo_tablespaces_active;
 extern unsigned long long	srv_max_undo_log_size;
 
 extern uint	srv_n_fil_crypt_threads;
-extern uint	srv_n_fil_crypt_threads_started;
+extern Atomic_relaxed<uint> srv_n_fil_crypt_threads_started;
 
 /** Enable or Disable Truncate of UNDO tablespace. */
 extern my_bool	srv_undo_log_truncate;

storage/innobase/row/row0import.cc

@@ -2317,7 +2317,6 @@ row_import_cleanup(row_prebuilt_t* prebuilt,
 	prebuilt->trx->op_info = "";
 
 	DBUG_EXECUTE_IF("ib_import_before_checkpoint_crash", DBUG_SUICIDE(););
-	fil_crypt_threads_signal();
 
 	if (err != DB_SUCCESS
 	    || !dict_table_get_first_index(table)->is_gen_clust()) {